The Court has had as many as ten justices (including the Chief Justice). Its current membership was set at nine in 1869.
FDR got mad because The Court kept voting against his New Deal legislation, so he hatched a scheme to add six more justices to The Court in the hopes of engineering a majority in his favor. His plan didn't work. I think he got the last laugh, since whenever he got the opportunity, he picked the youngest men he could find to appoint to The Court. William Douglas was his last appointee to "retire" in 1975. The sad thing about Justice Douglas is that due to his health, his mental capacity had diminished a great deal prior to his retirement.
He was a brilliant legal scholar when he was at the top of his game.
Yeah, I admit it. I am way too interested in Court trivia. Did you know that there was a justice who went back to law school for a refresher course after his appointment? He was afraid that he did not know enough law to serve on The Court.
The U.S. Supreme Court has nine members. They used to be called "The Nine Old Men" until Justice O'Connor joined the court. I guess now they are the "Seven Old Men and Two Ladies".